Project Setup

Let's create a simple Spring project to demonstrate AOP concepts.

Step-1: Create a maven project using Eclipse or Spring Tool Suite.

Group Id= org.apache.maven.archetypes 
Artifact Id= maven-archetype-quickstart
version= 1.1

Step-2: Add required dependencies in pom.xml.

        <dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-context</artifactId>
			<version>5.3.10</version>
		</dependency>
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-core</artifactId>
			<version>5.3.10</version>
		</dependency>

		<dependency>
			<groupId>org.aspectj</groupId>
			<artifactId>aspectjweaver</artifactId>
			<version>1.9.7</version>
		</dependency>

Step-3: Create a Spring Configuration file i.e. config.xml in the main class. This will be used to configure the Spring component and AOP aspects.

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:aop="http://www.springframework.org/schema/aop"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd">
        
    <aop:aspectj-autoproxy></aop:aspectj-autoproxy>
    
    <!-- bean definitions here -->
    
    <bean name="purchase" class="com.aop.aopexample.serviceimpl.PurchaseServiceImpl"/>
    <bean name="aspect" class="com.aop.aopexample.aspect.Aspect"/>

</beans>

Step-4: Create a Service Class.

package com.aop.aopexample.service;
public class PurchaseService {

	public void buyNow() {
		// your code
		System.out.println("Added to Cart!!");
		// your code
		System.out.println("Order Placed!!");
	}
}

Step-5: Create an Aspect Class.

package com.aop.aopexample.aspect;

import org.aspectj.lang.annotation.After;
import org.aspectj.lang.annotation.Before;

@org.aspectj.lang.annotation.Aspect
public class Aspect {

	@Before(value = "execution(* com.aop.aopexample.serviceimpl.PurchaseServiceImpl.buyNow())")
	public void printBefore() {
		System.out.println("Please Signin");
	}

	@After(value = "execution(* com.aop.aopexample.serviceimpl.PurchaseServiceImpl.buyNow())")
	public void printAfter() {
		System.out.println("Please Signout");
	}

}

Step-6: The Main Application Class

package com.aop.aopexample;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.aop.aopexample.service.PurchaseService;

public class App {
	public static void main(String[] args) {
		ApplicationContext context = new ClassPathXmlApplicationContext("com/aop/aopexample/config.xml");
		PurchaseService purchaseObject = context.getBean("purchase", PurchaseService.class);
		purchaseObject.buyNow();
	}
}

Step-7: Now Run the main class i.e. App.java

Here the Before Advice Execute first then the buyNow() method after that After Advice will be executed.

Output:

Please Signin  
Added to Cart!!
Order Placed!!
Please Signout